The P-rod tested out as follows (didn't record the whole 10-shot string)
lo = 716 FPS
hi = 738 FPS
av = 729 FPS
Es = 21.92
Sd = 7.81
These numbers with both adjustments full on, and a stock hammer spring; starting fill was 2600 PSI. My next testing won't come until I buy a chronograph, and install the Disco hammer spring I got from Gary. Overall, I'd call these numbers mediocre. But the advantage is not a lot more air being used versus the stock TP, so the shot count is still good; three magazines is livable for 17FPE.
edit: I forgot to post the video here so you can hear how quiet it is with Jim's shroud extension (spacer) at the breech end. It's very quiet for an average of 729FPS, imo. http://www.youtube.com/watch?v=EEbVmWK5tPg